(1.) Field of the Invention
This invention relates to electromagnetic clutches or brakes, and more particularly, spring-biased brakes.
(2.) Description of the Prior Art
In the prior art, spring engaged clutches and brakes were used in applications where it was desirable that the clutch or brake be engaged or coupled when there was an absence of electrical power. This is frequently referred to as a "fail-safe" design. A "fail-safe" clutch could be used, for example, in a cooling fan application where it is desirable to turn the fan on and off to control the temperature of a device, but in the event of a loss of control, it would be safer for the fan to be on continuously and over-cool. "Fail-safe" brakes are more common in their application to moving devices (elevators, fork trucks, computer disc drives, etc.) which are safer stopped than moving.
These brakes are constructed with one or more plates engaging one or more sets of brake shoes on a friction disc in the spring-biased position. There is a gap between the electromagnetic force portion and the plates. Due to the wear of the friction material on the brake pads, this gap increases with use. Accordingly, two frequently called for adjustments are adjustment of the spring force, which in turn assists braking torque, and adjustment of the air gap. The air gap adjustment is necessary when the gaps becomes so large that the plate will not disengage from the brake shoe due to insufficient magnetic force. At that point, either the friction disc of the brake must be replaced or the air gap adjusted.
Further in the prior art, it was known to make these adjustments independent of one another and at a plurality of locations as through the number of screws or adjustable springs.
It is desirable from a maintenance standpoint to provide a single point of adjustment and to combine these functions of adjustment of air gap and torque in a single integrated assembly.
It is further desirable that this assemblage provide for uniform application of force against the plate.
Accordingly, it is an object of this invention to provide a single assembly integrated adjustment device for air gap and braking torque.
It is a further object of this invention to provide such a device in which there is an independent control for the uniform application of force in the adjustment of torque uniformly about the plate and independently of the air gap adjustment mechanism which can operate coextensively with that mechanism.
It is a further object of this invention to reduce the number of moving parts necessary to accomplish this end.
These and other objects of this invention will become apparent from the following description with reference to the accompanying drawings.